Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S15/00—Systems using the reflection or reradiation of acoustic waves, e.g. sonar systems
  • G01S15/02—Systems using the reflection or reradiation of acoustic waves, e.g. sonar systems using reflection of acoustic waves
  • G01S15/06—Systems determining the position data of a target
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F41—WEAPONS
  • F41G—WEAPON SIGHTS; AIMING
  • F41G3/00—Aiming or laying means
  • F41G3/02—Aiming or laying means using an independent line of sight
• • G—PHYSICS
  • G06—COMPUTING; CALCULATING OR COUNTING
  • G06F—ELECTRIC DIGITAL DATA PROCESSING
  • G06F3/00—Input arrangements for transferring data to be processed into a form capable of being handled by the computer; Output arrangements for transferring data from processing unit to output unit, e.g. interface arrangements
  • G06F3/01—Input arrangements or combined input and output arrangements for interaction between user and computer
  • G06F3/03—Arrangements for converting the position or the displacement of a member into a coded form
  • G06F3/033—Pointing devices displaced or positioned by the user, e.g. mice, trackballs, pens or joysticks; Accessories therefor
  • G06F3/0346—Pointing devices displaced or positioned by the user, e.g. mice, trackballs, pens or joysticks; Accessories therefor with detection of the device orientation or free movement in a 3D space, e.g. 3D mice, 6-DOF [six degrees of freedom] pointers using gyroscopes, accelerometers or tilt-sensors
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10S367/00—Communications, electrical: acoustic wave systems and devices
  • Y10S367/907—Coordinate determination

Definitions

• the invention relates to a system for determining the position and orientation of an object and more particularly a method and apparatus for an acoustic based determination of an arbitrary position and orientation of an object in space without any physical tether or connection to the object and with no alignments or predetermined spatial relationships between the system and the target object.
• the first is the method employed by self-propelled weapon systems.
• Self propelled weapon systems use a three-axis attitude sensor and global positioning system (GPS) to determine pointing data.
• GPS global positioning system
• the second is a theoretical optical method.
• a barcode is attached to the end of the tube, and a barcode reader is used to measure the tube displacement and calculate azimuth.
• attitude sensor and GPS eliminates the need for a survey
• this method also has shortcomings.
• the primary shortcomings of the self-propelled pointing system are excess weight, and power requirements.
• a towed or man portable solution cannot accommodate the equipment used on the self-propelled system.
• the self propelled system is exposed to severe shock, vibration, and temperature, since it is mounted on the tube. This results in unacceptable failure rates of electronic components.
• the second method is a system using optics to perform weapon pointing.
• a barcode is attached to the end of the weapon's tube with a barcode reader placed a few meters away. As the tube is moved, the barcode reader picks up the displacement and performs the calculations to determine azimuth and elevation. Because this optical solution is theoretical, the accuracy requirements have not been proven.
• the current methods fail to address weight, power, accuracy, and off tube mounting requirements.
• U.S. Patent No. 4,853,863 to Cohen, et al. discloses a system that uses light, ultrasound and string wound on encoded, spring-loaded reels as mechanisms for calculations based on distances, angle measurements and doppler shift measurements (derivatives) which are then integrated to yield distance measurements.
• the Cohen, et al. system calls for 3 emitters and 3 detectors, all non-collinear for obtaining the measurements.
• the present invention utilizes 2 emitters (collinear) and 3 detectors (non-collinear).
• Another distinction from Cohen, et al. is that the present invention utilizes 6 distances coupled with a means of locating the system reference frame on the geodetic grid and a means of determining reference frame orientation to calculate absolute attitude and position. No such enhancement is to be found in Cohen, et al. In addition, Cohen, et al., does not reference fire control applications as disclosed herein.
• U.S. Patent No. 5,280,457 to Figueroa, et al. discloses a means for making absolute distance measurements using ultrasound and a "strobe" signal.
• the device is designed to eliminate the speed of sound as a system variable.
• Figueroa, et al. describes a means to locate a single point in 3- space, unlike the present invention which determines object position and orientation (6 degrees of freedom) in 3-space.
• Figueroa, et al. also describes, as a means to accomplish this, the use of one emitter and t?7+2 detectors to operate in m dimensions, i.e. one emitter and 5 detectors for a 3D system. Again, this is in contrast to the present invention, which uses 2 and 3 respectively.
• no application other than a self-calibrating means of locating a point is given Figueroa et al.
• the present system provides an easy to use means of making accurate determinations of an object's position and orientation.
• the object of interest can have an arbitrary orientation with respect to the sensing device.
• the user does not need to establish precise references or datum points when using the system.
• the Remote Attitude and Position Indicating Device is a system for determining the location and pointing attitude of an object relative to a known coordinate system.
• the RAPID system uses an ultrasonic based measurement technique to determine the distances from two points on the object of interest to at least three points forming a plane in the known coordinate system.
• the derivation of the minimum six distances is accomplished by transmitting a distinct acoustic signal from each of two emitters and deriving the time of flight of each distinct signal from the two detectors to at least three detectors.
• Measurement of time of flight relies on the fact that the acoustic signals travel at the speed of sound.
• TOF measurements requires that the detection algorithm (hardware and/or software) ascertain the instant when the acoustic signals were sent. This can be accomplished using an RF pulse transmission, which occurs at the same time as the acoustic pulse but is received instantaneously at the detector and its associated receiver electronics. Similar results can be obtained without a reference pulse by measuring the round trip time of flight, where three acoustic signals are transmitted to the two object transducers, conditioned and returned to the transmitting transducer after a fixed delay. Upon derivation of the minimum, six TOF values, six emitter/pair distances are computed, for use in final computation of object orientation using standard geometric equations.
• the method described above is implemented via two primary electronic assemblies. These consist of an emitter assembly and detector assembly. Note that there are two emitter assemblies on the object of interest.
• the emitter assembly contains the electronic circuitry necessary to generate the required drive signals for an acoustic emitter and the RF transceiver (in the case of the RF reference system).
• the detector assembly contains the electronic circuitry necessary to receive, amplify and process the signals detected by a minimum of three transducers. This circuitry may also include a RF transceiver for receipt of the "time sent" reference signal. In the round trip measurement implementation, the detector assembly would contain the electronics necessary to drive the dual purpose transducers, and then receive, amplify and process the returned signals.
• the detector assembly will accommodate an interface to a attitude and heading reference device to enable calculation of object orientation in a know coordinate system (earth frame).
• a primary object of the present invention is to enable automation of mortar laying, targeting and displacement.
• Another object of the present invention is to enhance the lethality of the mortar platform.
• Another object of the present invention is to connect the mortar to the digital battlefield.
• Another advantage of the present invention is since the primary electronics are not on the weapon, the environment is much more friendly, thereby reducing cost impacts of the environmental design requirements on the system
• Yet another advantage of the present invention is that the system is extremely light, further supporting its inclusion as part of the manpack and towed mortar systems
• Another advantage of the present invention is that the system does not require special setup or calibration, thereby improving operations and survivability
• Another advantage of the present invention is that the system accuracy is dependent on the accuracy of the pitch/roll/heading system, thereby offering tailorable performance and cost.
• Fig. 1 shows the preferred position and orientation sensing system.
• Fig. 2 schematically shows the preferred emitter assembly.
• Fig. 3 shows the preferred detector module.
• Fig. 4 shows the typical components in either of the embodiments of the invention.
• Fig. 5 is a flow chart showing a typical method of using the invention.
• the present invention comprises a system for determining an arbitrary position and orientation of an object in space without any physical tether or connection to the object and with no alignments or predetermined spatial relationships between the system and the target object.
• the preferred system is shown in Fig. 1.
• the object of interest 001 represents a mortar tube.
• This object 001 includes two acoustic emitter assemblies 100 mounted on the axis of the tube and separated by some know distance.
• the detector box and three associated transducers 200 are located at and establish the reference coordinate system for measurement of the tube attitude.
• the six measured distances between emitter/detector pairs are used to geometrically compute the pointing vector formed by the two emitters on the tube.
• the system comprises an emitter assembly 100 of Fig. 2 and a detection/processing module 200 of Fig. 3 and associated software.
• the emitter assembly 100 is comprised of two ultrasonic transducers 108, a short-range radio frequency transceiver 110, associated drive electronics 102, power supply 116 and RF antenna 106.
• the electronics 102 excite the ultrasonic transducers 108 at the required resonant frequency.
• the transmission of the two transducers 108 may be separated in phase or in frequency in order to distinguish the signals at the detectors.
• the circuitry also drives the RF transceiver 110 so that it emits a suitable radio frequency pulse 112.
• the electronics for the acoustic and radio frequency sub-circuits derive their timing from an oscillator 104 and the phase relationship between the RF 112 and the acoustic pulses 114 is known.
• the RF pulse 112 serves as a timing reference at the detector module 200 and allows emitter-to-detector distances to be calculated directly from the phase relationship of the detected RF and acoustic signals and known parameters such as the speed of sound in air.
• the detector/processing module 200 is comprised of three ultrasonic detectors 210, signal conditioning electronics 216, threshold detection circuitry 218, a short range RF transceiver 214, a processor sub-system 220 and 222 and antenna 212.
• a pitch/roll/heading sense sub-system 224 and 226 is required to enable absolute position and attitude information to be obtained at the detector/processing module 200.
• a GPS system and 'battlefield internet' capability would also be included.
• the meteorological data 228 is received via the 'battlefield internet'.
• the three ultrasonic detectors 210 are mounted on the module 200 such that they are not co- linear and thus they define a plane.
• the pitch/roll/heading sensors 224 and 226 are precision mounted in the module 200 with respect to this plane. Object position and orientation are referenced to the synthetic coordinate system established by the pitch/roll/heading sensors 224 and 226.
• the radio frequency pulse 230 is received at the detector module 200 and initializes the threshold detection and comparison process 220. Acoustic signals 240 are received and processed such that originating acoustic emitter is known.
• One possible embodiment of the detector design includes a timing circuit, (embodied within 220) where the high precision timer is triggered upon receipt of the RF reference pulse 230 and the time of flight measurement is obtained upon receipt of the acoustic pulses 240.
• a threshold detection technique 218 may be employed to determine the receipt of the acoustic pulse 240.
• the time interval relative to the RF pulse for time-of-flight from each of two emitters to each of three detectors results in a set of six distinct time intervals 250 for each measurement cycle. These intervals 250 are processed to determine six independent emitter-to-detector distances 250. In certain applications such as military applications, meteorological data 228 such as temperature, pressure and humidity can be factored into the distance determination to enhance accuracy.
• meteorological data 228 such as temperature, pressure and humidity can be factored into the distance determination to enhance accuracy.
• the set of all possible emitter locations that could generate a given distance result describe a sphere in the system reference frame. The intersection of three such spheres (one for each detector) is two points, only one of which is a logical solution. This solution is the location of the emitter that originated the acoustic pulses.
• the object's e.g. mortar tube
• the object's e.g. mortar tube
• one additional transform computation can be performed to map the system reference frame to the geodetic coordinate system employed in fire missions.
• the equations for computation of the vector pointing angles, azimuth, and elevation are:
• d1a (A0 2 + A1 2 + A2 2 ) 1/2
• d2a ((AO-R20) 2 + A1 2 + A2 2 ) 1 2
• d3a (AO 2 + (AO-R30) 2 + A2 2 ) 1/2
• d1 b (B0 2 + B1 2 + B2 2 ) 1 2
• d2b ((B0-R 20 ) 2 + B1 2 + B2 2 ) 1/2
• d3b (BO 2 + (B0-R 30 ) 2 + B2 2 ) 1/2
• R 2 o is distance between origin detector and detector on x axis
• R 30 is distance between origin detector and detector on y axis.
• the resulting distances (d1a, d2a, d3a, d1 b, d2b, d3b) are the coordinates for the emitters and azimuth and elevation is computed as follows:
• ⁇ xz arctan(Mtube2/MtubeO) - Elevation (4)
• This system could be implemented as a low cost solution with an existing off-the-self pitch/roll/heading module 224 and 226.
• a detector module 200 with an embedded Inertial Navigation System would provide enhanced precision, and could allow one INS to serve multiple weapons.
• the preliminary design of the system relied on the use of a phase locked loop (PLL) for acoustic pulse edge detection.
• PLL phase locked loop
• This implementation was intended to result in a very simplistic way of detecting the beginning and end of the acoustic pulse.
• the PLL was not stable enough to perform edge detection to the resolution required to obtain the distance measurement accuracy specified for the system.
• the design was changed to eliminate the PLL and the acoustic pulse was input to a fast A/D and processed via a digital signal processor. While other similar known techniques can be utilized, this technique allowed measurement of the pulse edge for TOF measurements to within 50 microseconds.
• This implementation yielded final azimuth and elevation computations to within 10 mils (0.56 degree) accuracy with averaging.
• the present invention will interface to GPS and pitch/roll/heading sensors 224 and 226 to provide the reference coordinate system and position information to the detector/processing module 200.
• the detector/processing module 200 will also be capable of interfacing to other systems, such as communication radios, which, in the case of the fire control system application, will provide meteorological data (not shown).
• the preferred embodiment of the system does not require a RF reference pulse.
• the desired distance measurements are derived through round trip measurement of the time of flight of a transmitted acoustic pulse.
• the typical components for the system are shown in Fig. 4.
• the transmitted pulses are received at the weapon system transducer 108, amplified 312, reshaped 314 and retransmitted back to the detector/processing module 400.
• the delay in the active electronics at the weapon system is fixed. Therefore, the distance is equal to half of the total time of flight, less the fixed delay in the electronics.
• the principal detector assembly drive electronics are the same.
• Transducers 108 when excited by an input signal produced by the drive electronics at the proper frequency produce an acoustic pulse at the resonant frequency of the transducers 108/210.
• the signal is received at the detecting transducer 210.
• the acoustic pulse excites the transducer 210 resulting in a voltage signal with characteristics corresponding to the frequency and amplitude of the signal received.
• This signal is conditioned and retransmitted (in the case of the preferred embodiment) or triggers the measurement of time of flight (in the case of RF reference pulse embodiment).
• the processing electronics/software captures the TOF measurement for each emitter-detector pair (or round trip TOF) and then computes the desired azimuth and elevation via a mathematical implementation of equations (1), (2), (3), and (4).
• the present invention is unique in its implementation for derivation of azimuth and elevation for a weapons system.
• the active reflector embodiment is also unique as it eliminates the need for a reference pulse from which to base time of flight. The time of flight is obtained purely from the acoustic signal.
• the transducers 210 may be driven in numerous ways to produce different characteristic signals.
• the pulse duration and shape may be altered to accommodate desired performance in range and signal decoding/integrity. This allows flexibility in both the drive and receive circuitry.
• the processing element may take several forms, including programmable logic devices, microprocessors and digital signal processors.
• the power supply could be batteries or other type of portable supply such as solar cells.
• the sensors and electronics may be combined to form an integrated package whose input is an unconditioned drive signal and whose output is a TOF measurement or a trigger indicating receipt of a valid acoustic pulse edge.
• Additional acoustic sensors may be added for use in calibration of speed of sound variations due to temperature and other air column effects. Additional sensors will also improve accuracy of measurement and eliminate ambiguities in coordinate position measurements.
• the RF transceivers may be eliminated in the active reflector embodiment. It is also possible to eliminate the need for a processor if the algorithms are implemented in hardware and/or firmware.
• the software and/or firmware in the system will support two functions in the system.
• the first function will be control of the hardware. This will include initialization and reset functions for such devices as analog to digital converters and time of flight measurement timer (if implemented in hardware).
• the software will then read the time of flight (TOF) measurements and compute the desired azimuth and elevation outputs per the equations (1), (2), (3), and (4). These equations form the algorithms for computation of the desired weapon pointing angles.
• the angles will be converted to the coordinate system of the pitch/roll/heading sensors 224 and 226 by the software.
• the software will also include a user interface function, which provides pointing cues to the weapons system operator. These cues will provide information for positioning the weapon at the correct attitude necessary to hit its target.
• Fig. 5 is a flow chart showing a typical method for using the preferred embodiment in a mortar tube application.
• Sensing the position/orientation of more than one mortar with a single detector module Sensing the position/orientation of more than one mortar with a single detector module.
• unique emitter carrier frequencies (or pulse trains) and complementary receiving electronics would allow more than one weapon to be served by a single detection module.
• the invention can be used on larger weapon systems, such as tank tubes.
• the system could replace the tube-droop sensing system (currently a laser/reflector/detector implementation) as well.

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• Engineering & Computer Science (AREA)
• General Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• Theoretical Computer Science (AREA)
• General Physics & Mathematics (AREA)
• Remote Sensing (AREA)
• Radar, Positioning & Navigation (AREA)
• Human Computer Interaction (AREA)
• Computer Networks & Wireless Communication (AREA)
• Acoustics & Sound (AREA)
• Measurement Of Velocity Or Position Using Acoustic Or Ultrasonic Waves (AREA)
• Navigation (AREA)
• Aiming, Guidance, Guns With A Light Source, Armor, Camouflage, And Targets (AREA)
• Selective Calling Equipment (AREA)
• Traffic Control Systems (AREA)

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• 2001
  • 2001-04-09 US US09/829,319 patent/US6456567B1/en not_active Expired - Lifetime
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